Cholesterol-binding motifs in STING that control endoplasmic reticulum retention mediate anti-tumoral activity of cholesterol-lowering compounds

The cGAS-STING pathway plays a crucial role in anti-tumoral responses by activating inflammation and reprogramming the tumour microenvironment. Upon activation, STING traffics from the endoplasmic reticulum (ER) to Golgi, allowing signalling complex assembly and induction of interferon and inflammatory cytokines. Here we report that cGAMP stimulation leads to a transient decline in ER cholesterol levels, mediated by Sterol O-Acyltransferase 1-dependent cholesterol esterification. This facilitates ER membrane curvature and STING trafficking to Golgi. Notably, we identify two cholesterol-binding motifs in STING and confirm their contribution to ER-retention of STING. Consequently, depletion of intracellular cholesterol levels enhances STING pathway activation upon cGAMP stimulation. In a preclinical tumour model, intratumorally administered cholesterol depletion therapy potentiated STING-dependent anti-tumoral responses, which, in combination with anti-PD-1 antibodies, promoted tumour remission. Collectively, we demonstrate that ER cholesterol sets a threshold for STING signalling through cholesterol-binding motifs in STING and we propose that this could be exploited for cancer immunotherapy.

Baseline serum levels of IgA anti-cyclic citrullinated protein antibodies in early rheumatoid arthritis predict radiographic progression after 11 years of treatment: a secondary analysis of the CIMESTRA study

OBJECTIVE

Smoking and periodontitis are risk factors for developing rheumatoid arthritis (RA), suggesting a break of tolerance on mucosal surfaces. Immunoglobulin A (IgA) antibodies are part of the mucosal immune system. The dominant autoantibodies in RA are anti-cyclic citrullinated protein antibodies (ACPAs), and IgG and IgA subclasses exist simultaneously. This study aimed to investigate the association of ACPA IgA subtypes with disease activity and long-term radiographic outcomes in RA, compared with ACPA IgG.

METHOD

Total ACPA IgG, IgA, IgA1, and IgA2 were quantified in serum from patients with early RA (n = 97). Patient characteristics, IgM rheumatoid factor (IgM-RF) status, clinical and biochemical disease activity scores, and radiographic status evaluated by total Sharp score (TSS), were assessed at baseline and after 2 and 11 years of treatment.

RESULTS

All patients with ACPA IgA also had ACPA IgG. ACPA IgA positivity was associated with IgM-RF and male gender. Both ACPA IgA and IgG levels at baseline were weakly associated with disease activity markers. Baseline ACPA IgA and IgG did not show a linear correlation with radiographic status after 10 years, but could predict radiographic progression (ΔTSS ≥ 5 from 0 to 11 years), with positive likelihood ratios of 3.7 and 4.0, respectively.

CONCLUSION

ACPA IgA and IgG were weakly associated with disease activity in early RA. RA patients with a ΔTSS ≥ 5 after 11 years of treatment had higher ACPA IgG and ACPA IgA levels at baseline; however, none of the ACPA subtypes was superior in predicting long-term radiographic progression.

T-cell derived extracellular vesicles prime macrophages for improved STING based cancer immunotherapy

A key phenomenon in cancer is the establishment of a highly immunosuppressive tumour microenvironment (TME). Despite advances in immunotherapy, where the purpose is to induce tumour recognition and hence hereof tumour eradication, the majority of patients applicable for such treatment still fail to respond. It has been suggested that high immunological activity in the tumour is essential for achieving effective response to immunotherapy, which therefore have led to exploration of strategies that triggers inflammatory pathways. Here activation of the stimulator of interferon genes (STING) signalling pathway has been considered an attractive target, as it is a potent trigger of pro-inflammatory cytokines and types I and III interferons. However, immunotherapy combined with targeted STING agonists has not yielded sustained clinical remission in humans. This suggests a need for exploring novel adjuvants to improve the innate immunological efficacy. Here, we demonstrate that extracellular vesicles (EVs), derived from activated CD4+ T cells (T-EVs), sensitizes macrophages to elevate STING activation, mediated by IFNγ carried on the T-EVs. Our work support that T-EVs can disrupt the immune suppressive environment in the tumour by reprogramming macrophages to a pro-inflammatory phenotype, and priming them for a robust immune response towards STING activation.

MYC Overexpression Drives Immune Evasion in Hepatocellular Carcinoma That Is Reversible through Restoration of Proinflammatory Macrophages

Cancers evade immune surveillance, which can be reversed through immune-checkpoint therapy in a small subset of cases. Here, we report that the MYC oncogene suppresses innate immune surveillance and drives resistance to immunotherapy. In 33 different human cancers, MYC genomic amplification and overexpression increased immune-checkpoint expression, predicted nonresponsiveness to immune-checkpoint blockade, and was associated with both Th2-like immune profile and reduced CD8 T-cell infiltration. MYC transcriptionally suppressed innate immunity and MHCI-mediated antigen presentation, which in turn impeded T-cell response. Combined, but not individual, blockade of PDL1 and CTLA4 could reverse MYC-driven immune suppression by leading to the recruitment of proinflammatory antigen-presenting macrophages with increased CD40 and MHCII expression. Depletion of macrophages abrogated the antineoplastic effects of PDL1 and CTLA4 blockade in MYC-driven hepatocellular carcinoma (HCC). Hence, MYC is a predictor of immune-checkpoint responsiveness and a key driver of immune evasion through the suppression of proinflammatory macrophages. The immune evasion induced by MYC in HCC can be overcome by combined PDL1 and CTLA4 blockade.

SIGNIFICANCE

Macrophage-mediated immune evasion is a therapeutic vulnerability of MYC-driven cancers, which has implications for prioritizing MYC-driven hepatocellular carcinoma for combination immunotherapy.

Experiences, perspectives, and practice patterns of pulmonary embolism follow-up in Denmark. A mixed method study informing the development of A sTrucTurEd INtegrateD post PE care model

Background

Practice patterns of follow-up after pulmonary embolism (PE) varies both within and between countries, and high-quality evidence to provide clinical guidance is lacking [1,2]. This study is part of the trial – A sTrucTurEd INtegrateD post Pulmonary Embolism care model (Attend-PE) aimed at developing and testing the effectiveness of a structured, integrated and patient-centered follow-up care model for patients with PE.

Purpose

To explore experiences, perspectives, and practice patterns of PE follow-up. Ultimately identifying and describing the opportunity space for a structured integrated post PE care model.

Methods

We performed a convergent mixed method study based on data from patient journey mapping including surveys, observations, and semi-structured patient interviews across all main hospitals treating PE in Denmark. An integrated mixed methods interpretation was conducted using joint displays.

Results

Main results are presented in joint displays in Figure 1 and 2. Observations and surveys were conducted at 18 hospitals including 12 in-depth patient-interviews.

The structure of care varied greatly. Patients expressed a need for early follow up and specialist care but at 18% of the sites first follow-up visit was not until 3–6 months after PE and 24% of the sites only had in-person contact with patients when follow-up echocardiography was needed. At some sites it was also highlighted that not all patients were referred to the post PE follow-up. anticoagulation clinics. Further, transition of care to the general practitioner was identified as a particular challenge.

All sites considered Non-vitamin K antagonist oral anticoagulants the preferred anticoagulant treatment with low-molecular-weight heparins/Vitamin K antagonists as second choice. The possible need for extended treatment and reduced dose favored Rivaroxaban and Apixaban. The decision on treatment duration was most often taken at the 3–6-month follow-up visit, and patients described the decision on extended treatment as positive and reassuring.

Patient information (oral and written) varied greatly and was most often focused on anticoagulant treatment, while knowledge on PE in general, symptom management, and activity was scarce. Two sites offered structured group-based patient education, but unstructured patient education at the individual follow-up visits was most common.

Help and guidance on managing post-PE symptoms and returning to everyday life was perceived essential by patients, as it affected them both physically and mentally. However, none of the sites routinely offered or referred patients to rehabilitation.

Involvement of relatives was considered important but 33% of the hospital sites did not systematically encourage relatives to attend follow-up.

Conclusion

The considerable variation in structure of PE follow-up care demonstrated in this mixed method study highlights the need for a structured integrated post pulmonary embolism care model.

Funding Acknowledgement

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): The Danish Heart AssociationThe Novo Nordisk Foundation

T-cell immunoglobulin and mucin domain 3 is upregulated in rheumatoid arthritis, but insufficient in controlling inflammation

OBJECTIVES

Rheumatoid arthritis (RA) is a chronic autoimmune disease, that involves both pro- and anti-inflammatory mechanisms. The purpose of the present study is to investigate T-cell immunoglobulin and mucin domain 3 (Tim-3) in RA.

METHODS

Plasma levels of soluble (s) Tim-3 in early RA (n=98), were followed, to evaluate association with treatment and disease activity, acquired from a prospective collected biobank (clinicaltrials.gov (NCT00660647)). We also investigate the influence of Tim-3 on spontaneous cytokine production in synovial fluid mononuclear cells (SFMC) from RA patients after addition of neutralizing anti-Tim-3's antibodies, either alone or in combination with neutralizing anti-Programmed Cell death protein 1 (PD-1) antibodies.

RESULTS

Long-time stimulated CD4 T-cells expressed high levels of Tim-3, but tended to decrease their PD-1 expression. Tim-3 expression was exclusively seen co-expressed with PD-1 by CD3, CD4, CD45RO positive cells in the inflamed RA joint. Addition of neutralizing Tim-3 antibodies increased the secretion of IFNγ and MCP-1, in SFMC cultures from RA. Whereas neutralizing anti-PD-1 antibodies showed a broader impact on cytokine production. Finally, we observed that soluble Tim-3 is increased in plasma and is associated with disease activity in early RA.

CONCLUSION

Taken together, our findings indicate disease-suppressive functions of Tim-3 in RA.

MYC functions as a switch for natural killer cell-mediated immune surveillance of lymphoid malignancies

The MYC oncogene drives T- and B- lymphoid malignancies, including Burkitt's lymphoma (BL) and Acute Lymphoblastic Leukemia (ALL). Here, we demonstrate a systemic reduction in natural killer (NK) cell numbers in SRα-tTA/Tet-O-MYCON mice bearing MYC-driven T-lymphomas. Residual mNK cells in spleens of MYCON T-lymphoma-bearing mice exhibit perturbations in the terminal NK effector differentiation pathway. Lymphoma-intrinsic MYC arrests NK maturation by transcriptionally repressing STAT1/2 and secretion of Type I Interferons (IFNs). Treating T-lymphoma-bearing mice with Type I IFN improves survival by rescuing NK cell maturation. Adoptive transfer of mature NK cells is sufficient to delay both T-lymphoma growth and recurrence post MYC inactivation. In MYC-driven BL patients, low expression of both STAT1 and STAT2 correlates significantly with the absence of activated NK cells and predicts unfavorable clinical outcomes. Our studies thus provide a rationale for developing NK cell-based therapies to effectively treat MYC-driven lymphomas in the future.

CD46 activation induces distinct CXCL-10 response in monocytes and monocyte-derived dendritic cells

CD46 is an important immune regulatory receptor with dual functions, however, the CD46 isoform distribution and the effect of CD46 activation on the cytokine production in monocytes and monocyte-derived dendritic cells (moDCs) is unclear. Here, we show that CD46 activation of moDCs downregulates LPS-induced CXCL-10 expression, while the expression of CXCL-10 in monocytes is unaffected. Furthermore, the differentiation of moDCs induces a switch towards dominance of CYT-2 isoforms of CD46. These data indicate that CD46 activation exerts different functions in monocytes and moDCs and this correlates with a switch in CD46 isoform expression upon differentiation of moDCs.

CD46 is a potent co-stimulatory receptor for expansion of human IFN-γ-producing CD8+ T cells

Similar to CD4⁺ T cells, precursor CD8⁺ T cells are thought to depend on a co-stimulatory signal through CD28 for proliferation and differentiation into effector cells. CD46 is another co-stimulatory receptor that promotes differentiation of CD4⁺ T-helper cells type 1 (Th1 cells) into a regulatory phenotype with a switch from IFN-γ towards IL-10-secretion over time. Whether CD46 exerts a similar function on CD8⁺ T cells remains to be fully elucidated. Here, we demonstrate that CD46 co-stimulation induced secretion of IFN-γ as well as expansion of IFN-γ-secreting CD8⁺ T cells. In contrast to CD46 co-stimulation of CD4⁺ T cells, CD8⁺ T cells did not differentiate into a regulatory IL-10-secreting phenotype. This demonstrates that CD46 is a co-stimulatory receptor on CD8⁺ T cells, and that it exerts separate functions during CD4⁺ and CD8⁺ T-cell differentiation.

Extracellular Vesicles Transfer the Receptor Programmed Death-1 in Rheumatoid Arthritis

Introduction

Extracellular vesicles (EVs) have been recognized as route of communication in the microenvironment. They transfer proteins and microRNAs (miRNAs) between cells, and possess immunoregulatory properties. However, their role in immune-mediated diseases remains to be elucidated. We hypothesized a role for EVs in the rheumatoid arthritis (RA) joint, potentially involving the development of T cell exhaustion and transfer of the co-inhibitory receptor programmed death 1 (PD-1).

Methods

Synovial fluid mononuclear cells (SFMCs) and peripheral blood mononuclear cells (PBMCs) from RA patients were investigated for PD-1 and other markers of T cell inhibition. EVs were isolated from RA plasma and synovial fluid. In addition, healthy control (HC) and RA PBMCs and SFMCs were cultured to produce EVs. These were isolated and investigated by immunogold electron microscopy (EM) and also co-cultured with lymphocytes and PD-1 negative cells to investigate their functions. Finally, the miRNA expression profiles were assessed in EVs isolated from RA and HC cell cultures.

Results

Cells from the RA joint expressed several T cell co-inhibitory receptors, including PD-1, TIM-3, and Tigit. ELISA demonstrated the presence of PD-1 in EVs from RA plasma and synovial fluid. Immunogold EM visualized PD-1 expression by EVs. Co-culturing lymphocytes and the PD-1 negative cell line, U937 with EVs resulted in an induction of PD-1 on these cells. Moreover, EVs from RA PBMCs increased proliferation in lymphocytes when co-cultured with these. All EVs contained miRNAs associated with PD-1 and other markers of T cell inhibition and the content was significantly lower in EVs from RA PBMCs than HC PBMCs. Stimulation of the cells increased the miRNA expression. However, EVs isolated from stimulated RA SFMCs did not change their miRNA expression profile to the same extend.

Conclusion

EVs carrying both the PD-1 receptor and miRNAs associated with T cell inhibition were present in RA cell cultures. Upon stimulation, these miRNAs failed to be upregulated in EVs from RA SFMCs. This was in line with increased expression of T cell co-inhibitory markers on SFMCs. In conclusion, we suggest EVs to play a significant role in the RA microenvironment, potentially favoring the progression of T cell exhaustion.

CD46 activation on monocyte-derived dendritic cells

Objective

CD46 is an important immune modulatory receptor that influences the expression of certain cytokines in different cell types. This function has been proposed to depend on expression of specific isoforms of CD46. The common isoforms are named BC1, BC2, C1 and C2, and activation of T cells induces a switch towards dominance of BC2 and C2. However, the effect of CD46 activation on the cytokine production in dendritic cells (DCs) has so far been inconclusive and the relative distribution of CD46 isoforms in monocytes and DCs is unknown.

Methods

Monocytes were isolated from peripheral mononuclear blood cells and differentiated to dendritic cells (moDC). The maturation of moDCs was confirmed by flow cytometry using a panel of maturation markers. Monocytes and moDCs were stimulated with LPS in presence or absence of CD46 activation and the production of various cytokines were analyzed by real-time PCR. The monocytes and moDCs were furthermore analyzed for their expression of different CD46 isoforms by an isoform-specific real-time PCR assay.

Results

Upregulation of CD40, CD80, and CD83 on the surface of moDCs demonstrated the maturation of monocytes to moDCs. Activation of CD46 in moDCs during LPS stimulation was found to reduce the mRNA expression of IL12p40 and CXCL10 while no effect of CD46 activation on these cytokines was observed in monocytes. Examination of CD46 isoforms revealed a dominant expression of the isoforms BC2/C2 in moDCs upon differentiation from monocytes.

Conclusion

The results presented here suggest that CD46 activation reduces the pro-inflammatory potential of LPS stimulation in moDCs but not in monocytes. These functional changes are associated with a switch towards dominant expression of BC2/C2 isoforms.

Divergent tropism of HHV-6AGS and HHV-6BPL1 in T cells expressing different CD46 isoform patterns

CD46 is a receptor for HHV-6A, but its role as a receptor for HHV-6B is controversial. The significance of CD46 isoforms for HHV-6A and HHV-6B tropism is unknown. HHV-6A_GS was able to initiate transcription of the viral genes U7 and U23 in the CD46⁺CD134^- T-cell lines Peer, Jurkat, Molt3, and SupT1, whereas HHV-6B_PL1 was only able to do so in Molt3 and SupT1, which expressed a CD46 isoform pattern different from Peer and Jurkat. The HHV-6B_PL1-susceptible T-cell lines were characterized by low expression of the CD46 isoform BC2 and domination of isoforms containing the cytoplasmic tail, CYT-1. A HHV-6B_PL1 susceptible cell line, Be13, changed over time its CD46 isoform pattern to resemble Peer and Jurkat and concomitantly lost its susceptibility to HHV-6B_PL1 but not HHV-6A_GS infection. We propose that isoforms of CD46 impact on HHV-6B infection and thereby in part explain the distinct tropism of HHV-6A_GS and HHV-6B_PL1.

Non-random pairing of CD46 isoforms with skewing towards BC2 and C2 in activated and memory/effector T cells

CD46 is a glycoprotein with important functions in innate and adaptive immune responses. Functionally different isoforms are generated by alternative splicing at exons 7–9 (BC and C isoforms) and exon 13 (CYT-1 and CYT-2 isoforms) giving rise to BC1, BC2, C1 and C2. We developed a novel real-time PCR assay that allows quantitative comparisons between these isoforms. Their relative frequency in CD4⁺ T cells from 100 donors revealed a distribution with high interpersonally variability. Importantly, the distribution between the isoforms was not random and although splicing favoured inclusion of exon 8 (BC isoforms), exclusion of exon 8 (C isoforms) was significantly linked to exclusion of exon 13 (CYT-2 isoforms). Despite inter-individual differences, CD4⁺ and CD8⁺ T cells, B cells, NK cells and monocytes expressed similar isoform profiles intra-individually. However, memory/effector CD4⁺ T cells had a significantly higher frequency of CYT-2 when compared with naïve CD4⁺ T cells. Likewise, in vitro activation of naïve and total CD4⁺ T cells increased the expression of CYT-2. This indicates that although splicing factors determine a certain expression profile in an individual, the profile can be modulated by external stimuli. This suggests a mechanism by which alterations in CD46 isoforms may temporarily regulate the immune response.

Assessing peristomal skin changes in ostomy patients: validation of the Ostomy Skin Tool

BACKGROUND

Peristomal skin problems are common and are treated by a variety of health professionals. Clear and consistent communication among these professionals is therefore particularly important. The Ostomy Skin Tool (OST) is a new assessment instrument for the extent and severity of peristomal skin conditions. Formal tests of reliability and validity are necessary for its use in clinical practice, research, and education.

OBJECTIVES

To estimate inter- and intra nurse assessment variability of the OST and validity by comparison to a 'gold standard' (GS) defined by an expert panel.

METHODS

Thirty photographs of peristomal skin were presented twice to 20 ostomy care nurses--10 from Denmark (DK) and 10 from Spain (ES)--to determine intra- and inter nurse assessment variability. The same photographs were presented to an international group of experts (dermatologist and ostomy care nurses), to establish a GS for comparison and validation of the results.

RESULTS

A high intra-nurse assessment agreement, κ=0·84, was found with no differences in the intra-nurse assessments from the two groups of nurses (DK and ES). The inter-nurse assessment agreement was 'moderate to good', κ=0·54, with the agreement between the experts higher, κ=0·70. A high correlation between the scores from the nurses and the GS were seen in the lower part of the two scales [Discoloration, Erosion, Tissue overgrowth (DET) score<7)].

CONCLUSION

The study supported the validity of the OST. It is suggested that a categorical scale can be used to illustrate the severity of the DET scores.

Effect of red wine and red grape extract on blood lipids, haemostatic factors, and other risk factors for cardiovascular disease

OBJECTIVE

Some epidemiological studies found a lower risk of cardiovascular disease among wine drinkers than among drinkers of other types of ethanol. This difference might be due to an effect of nonalcohol compounds in wine on important cardiovascular risk factors. The objective of this study was to compare the effect of red wine, nonalcohol compounds of red wine and placebo on established cardiovascular risk factors.

DESIGN

A parallel, four-armed intervention study.

SUBJECTS

A total of 69 healthy 38-74-y-old men and women.

INTERVENTIONS

Subjects were randomised to either 1: red wine (males: 300 ml/day, 38.3 g alcohol/day, female subjects: 200 ml/day, 25.5 g alcohol/day), 2: water + red grape extract tablets (wine-equivalent dose), 3: water + red grape extract tablets (half dose), or 4: water + placebo tablets for a period of 4 weeks. No other sources of alcohol or anthocyanin were allowed. Plasma high-density lipoprotein (HDL)-cholesterol (HDL-C), low-density lipoprotein (LDL)-cholesterol (LDL-C), HDL-C/LDL-C-ratio, very-low-density lipoprotein (VLDL)-triacylglycerol, total cholesterol, fibrinogen, factor VII coagulant activity (FVIIc), blood pressure, and body weight were determined before and after intervention.

RESULTS

Wine consumption was associated with a significant 11-16% increase in fasting HDL-C and 8-15% decrease in fasting fibrinogen relative to not drinking wine. There were no significant treatment effects on fasting LDL-C, HDL-C/LDL-C-ratio, VLDL-triacylglycerol, total cholesterol, FVIIc, or blood pressure. Drinking wine was associated with relative body weight increments closely corresponding to the energy contributed by the alcohol component.

CONCLUSION

Moderate red wine consumption for 4 weeks is associated with desirable changes in HDL-C and fibrinogen compared with drinking water with or without red grape extract. The impact of wine on the measured cardiovascular risk factors thus seems primarily explained by an alcohol effect. Our finding suggests that the putative difference in cardiac risk associated with wine vs other alcoholic beverages might be rather explained by other life-style confounders than by red wine contents of nonalcohol components.

Effect of 8 week intake of probiotic milk products on risk factors for cardiovascular diseases

OBJECTIVE

To investigate the effect of a probiotic milk product containing the culture CAUSIDO(R) and of two alternative products on risk factors for cardiovascular disease in overweight and obese subjects.

DESIGN

An 8 week randomized, double-blind, placebo- and compliance-controlled, parallel study.

SUBJECTS

Seventy healthy, weight-stable, overweight and obese (25.0<BMI<37.5 kg/m2) males (n=20) and females (n=50), 18-55 y old, were randomly assigned into five groups.

INTERVENTION

Four groups consumed 450 ml fermented milk products (yoghurt) daily. Group 1: a yoghurt fermented with two strains of Streptococcus thermophilus and two strains of Lactobacillus acidophilus (StLa). Group 2: a placebo yoghurt fermented with delta-acid-lactone (PY). Group 3: a yoghurt fermented with two strains of Streptococcus thermophilus and one strain of Lactobacillus rhamnosus (StLr). Group 4: a yoghurt fermented with one strain of Enterococcus faecium and two strains of Streptococcus thermophilus (CAUSIDO(R) culture), GAIO(R) (G). The dietary composition of the yoghurt was otherwise similar. The fifth group was given two placebo pills (PP) daily.

RESULTS

When comparing all five treatment groups, unadjusted for changes in body weight, no statistical effects were observed in week 8 in the G-group on low density lipoproteins (LDL)-cholesterol (P=0.29). After adjustment for small changes in body weight, LDL-cholesterol decreased by 8.4% (0.26+/-0.10 mmol/l; P<0.05) and fibrinogen increased (0.74+/-0.32 mmol/l; P<0.05) after 8 weeks in the G-group. This was significantly different from the group consuming chemically fermented yoghurt and the group consuming placebo pills (P<0.05). After 8 weeks, systolic blood pressure was significantly more reduced in the StLa and G-group compared to StLr. No other differences were found.

CONCLUSION

The CAUSIDO(R) culture reduced LDL-cholesterol and increased fibrinogen in the overweight subjects at a 450 ml consumption daily for 8 weeks. The effect on LDL-cholesterol confirms previous studies. An immunostimulation by one of the strains in the product might explain the effect on fibrinogen in the G-group.

SPONSORSHIP

MD Foods A/S, Denmark.

A quantitative assay to measure the interaction between immunogenic peptides and purified class I major histocompatibility complex molecules

A direct and sensitive biochemical assay to measure the interaction in solution between peptides and affinity-purified major histocompatibility complex (MHC) class I molecules has been generated. Specific binding reflecting the known class I restriction of cytotoxic T cell responses was obtained. Adding an excess of beta 2-microglobulin (beta 2m) significantly increased the rate of peptide association, but it did not affect the rate of dissociation. Binding was complicated by a rapid and apparently irreversible loss of functional MHC class I at 37 degrees C which might limit the life span of empty MHC class I thereby preventing the inadvertent exchange of peptides at the target cell surface. All class I molecules tested bound peptides of the canonical octa- to nona-meric length. However, one class I molecule, Kk, also bound peptides, which were much longer suggesting that the preference of class I molecules for short epitopes is not absolute and may be caused by factors other than the peptide-MHC class I binding event itself.

The interaction between beta 2-microglobulin (beta 2m) and purified class-I major histocompatibility (MHC) antigen

The function of MHC class-I molecules is to sample peptides from the intracellular environment and present them to CD8+ cytotoxic T lymphocytes. To understand the molecular details of the assembly (and disassembly) of peptide-beta 2m-class-I complexes a biochemical peptide-class-I binding assay has been generated recently and this paper reports on a similar assay for the interaction between beta 2m and class I. As a model system human beta 2m binding to mouse class I was used. The assay is strictly biochemical using purified reagents which interact in solution and complex formation is determined by size separation. It is specific and highly sensitive. The observed affinity of the interaction, KD, is close to 0.4 nM. The rate of association at 37 degrees C is very fast (the ka is around 5 x 10(4)/M/s) whereas the dissociation is slow (the kd is around 8 x 10(-6)/s); the ratio of dissociation to association yields a calculated KD close to the observed value. At 37 degrees C almost all of the purified class I participates in binding of the exogenously offered beta 2m showing that a considerable exchange of the endogenous beta 2m occurs. Finally, it was demonstrated that exogenous beta 2m enhances binding to MHC class-I of short perfectly-matching peptides as well as longer peptides.

A mouse aminopeptidase N is a marker for antigen-presenting cells and appears to be co-expressed with major histocompatibility complex class II molecules

To analyze the expression of mouse aminopeptidase N (APN) on the cells of the immune system a panel of rat monoclonal antibodies against mouse intestinal APN was generated. These antibodies were used to affinity purify functional mouse APN from both intestine and kidney, and by flow cytometry to examine the APN expression of the cells of the mouse immune system. An APN closely related, perhaps identical, to the intestinal APN was expressed on a subpopulation of spleen cells and stimulated peritoneal exudate cells, primarily representing antigen-presenting cells, such as B cells, macrophages, dendritic cells, and veiled cells. In contrast this APN expression could not be detected on thymocytes or spleen T cells. As a corollary, APN was expressed on monocyte, macrophage, and B lymphoma cell lines, but not on T hybridoma or thymoma cell lines. The expression of APN showed a striking correlation with the MHC class II expression in all the cell populations studied. This apparent co-expression suggests a role for APN in antigen processing.

MHC molecules protect T cell epitopes against proteolytic destruction

There is a subtle duality in the role of proteolytic enzymes in Ag processing. They are required to fragment protein Ag ingested by APC. However, prolonged exposure to proteolytic enzymes may lead to a complete degradation of the Ag, leaving nothing for the T cell system to recognize. What ensures that some of the Ag is salvaged? Using a cell-free system we demonstrate that an Ag fragment, once bound to a MHC class II molecule, is effectively protected against proteolytic destruction by cathepsin B and pronase E. The bound fragment, however, can be modified by aminopeptidase N. We suggest that MHC class II molecules play an important regulatory role in the physiologic processing of Ag.

MHC molecules protect T cell epitopes against proteolytic destruction

There is a subtle duality in the role of proteolytic enzymes in Ag processing. They are required to fragment protein Ag ingested by APC. However, prolonged exposure to proteolytic enzymes may lead to a complete degradation of the Ag, leaving nothing for the T cell system to recognize. What ensures that some of the Ag is salvaged? Using a cell-free system we demonstrate that an Ag fragment, once bound to a MHC class II molecule, is effectively protected against proteolytic destruction by cathepsin B and pronase E. The bound fragment, however, can be modified by aminopeptidase N. We suggest that MHC class II molecules play an important regulatory role in the physiologic processing of Ag.

pH dependence of the interaction between immunogenic peptides and MHC class II molecules. Evidence for an acidic intracellular compartment being the organelle of interaction

The pH dependence of the interaction between immunogenic peptide and MHC class II was studied both in a direct biochemical binding assay and in a functional Ag presentation assay. The two approaches yielded similar results. All of the peptides tested bound optimally to their relevant MHC class II restriction element at around pH 4.5. Indeed, several of the peptides did not bind at neutral pH. These results demonstrate that Ag under physiologic conditions meet MHC class II in a quite acidic environment. The very acidic pH optimal for peptide-MHC class II interaction is only found intracellularly and most notably in the endosome-lysosome compartment in which Ag processing is thought to occur. Thus, Ag processing and interaction with MHC class II molecules can potentially happen in the very same compartment. This yet undefined acidic compartment would have to contain proteolytic enzymes and MHC class II molecules.

pH dependence of the interaction between immunogenic peptides and MHC class II molecules. Evidence for an acidic intracellular compartment being the organelle of interaction

The pH dependence of the interaction between immunogenic peptide and MHC class II was studied both in a direct biochemical binding assay and in a functional Ag presentation assay. The two approaches yielded similar results. All of the peptides tested bound optimally to their relevant MHC class II restriction element at around pH 4.5. Indeed, several of the peptides did not bind at neutral pH. These results demonstrate that Ag under physiologic conditions meet MHC class II in a quite acidic environment. The very acidic pH optimal for peptide-MHC class II interaction is only found intracellularly and most notably in the endosome-lysosome compartment in which Ag processing is thought to occur. Thus, Ag processing and interaction with MHC class II molecules can potentially happen in the very same compartment. This yet undefined acidic compartment would have to contain proteolytic enzymes and MHC class II molecules.

Efficacy of HLö-7 and pyrimidoxime as antidotes of nerve agent poisoning in mice

The toxicity and efficacy of two oximes, HLö-7 and pyrimidoxime, were evaluated in mice and compared to those obtained with HI-6. HLö-7 and pyrimidoxime produced 24 h LD50 values of 356 and 291 mg/kg (i.p.), respectively. In combination with atropine (17.4 mg/kg, i.p.), HLö-7 was a very efficient therapy against poisoning by 3 x LD50 dose of soman, sarin and GF and 2 x LD50 dose of tabun with ED50 values of 12.4, 0.31, 0.32 and 25.2 mg/kg, respectively. In contrast, pyrimidoxime was a relatively poor therapy which resulted in ED50 values of greater than 150, 5.88, 100 and 71 mg/kg against poisoning by soman, sarin, GF and tabun, respectively. HLö-7 produced significant (p less than 0.05) reactivation of phosphorylated acetylcholinesterase, in vivo, resulting in 47, 38, 27 and 10% reactivation of sarin, GF, soman and tabun inhibited mouse diaphragm acetylcholinesterase, respectively. HLö-7 also antagonized sarin-induced hypothermia in mice suggesting that it reactivated central acetylcholinesterase. The potential of HLö-7 as a replacement oxime for the treatment of nerve agent poisoning is discussed.

Comparison of several oximes against poisoning by soman, tabun and GF

Three oximes currently being evaluated for adoption as replacement nerve agent therapy by various countries were compared for therapeutic efficacy against the toxic organophosphate inhibitors soman and tabun under a standard set of conditions. These oximes together with PAM-Cl and toxogonin, were also compared for efficacy against GF, an agent weaponized by Iraq. The order of effectiveness against soman was HI-6 greater than HLö-7 greater than pyrimidoxime. HLö-7 was very effective against tabun poisoning while HI-6 and pyrimidoxime were of moderate value. Against GF, HI-6 and HLö-7 were extremely effective, toxogonin was moderately effective, and PAM-Cl and pyrimidoxime were the least effective. HI-6 provided a high level of protection against all of the agents tested as did HLö-7 to a slightly lesser degree. The other oximes suffered from their lack of effects against one or more of the organophosphates.

Toxicity of organophosphate nerve agents and related phosphonylated oximes compared to their anticholinesterase activity in neuron cultures

Oximes, such as pralidoxime and toxogonin, are important therapeutic agents for the treatment of organophosphate (OP) nerve agent poisoning. Oximes can react with these nerve agents to give intermediates, phosphonylated oximes, which may be equally toxic to the parent OP. The sc LD50s of a series of phosphonylated 2-butanone and 2,3-butanedione monoximes were compared to the sc LD50s of their parent OPs (tabun, sarin, and VX) in CD-1 mice. In every case the derivatives were significantly less toxic than their parent nerve agents. Times to death, and to signs of poisoning, were inversely proportional to the dose of test compound, and in all mortalities, blood serum acetylcholinesterase (AChE) was severely inhibited. The relative potencies of these compounds, as well as soman, cyclohexyl methylphosphonofluoridate, and diisopropyl fluorophosphate, as inhibitors of AChE in primary cultures of mouse embryo neurons, correlated with their in vivo toxicities. The results indicate that mouse embryo neuron cultures may be a useful model with which to study this class of compounds.